As part of the Metainfo Refactoring, we need to make the Metainfo Loop
working with both the current PointerDB and the new Metabase. Thus, the
Metainfo Loop should pass to the Observer interface more specific Object
and Segment types instead of pb.Pointer.
After this change, there are still a couple of use cases that require
access to the pb.Pointer (hence we have it as a field in the
metainfo.Segment type):
1. Expired Deletion Service
2. Repair Service
It would require additional refactoring in these two services before we
are able to clean this.
Change-Id: Ib3eb6b7507ed89d5ba745ffbb6b37524ef10ed9f
* Added a gc package at satellite/gc, which contains the gc.Service, which runs garbage collection integrated with the metainfoloop, and the gc PieceTracker, which implements the metainfo loop Observer interface and stores all of the filters (about which pieces are good) for each node.
* Added a gc config located at satellite/gc/service.go (loop disabled by default in release)
* Creates bloom filters with pieces to be retained inside the metainfo loop
* Sends RetainRequests (or filters with good piece ids) to all storage nodes.
